The present invention relates to silicone polymer fluids which are useful as hydraulic fluids and more particularly the present invention relates to silicone polymer fluids wherein an MDT type silicone base fluid is combined with an alkyl siloxane-alkoxy siloxane copolymer which has polymeric units exhibiting difunctionality and/or trifunctionality.
Most brake fluids which are presently sold are glycol based polyethers which vary according to the type and number of polyether units in the polymer chain. Although such brake fluids have found wide acceptance for use in vehicles such as automobiles, such glycol based fluids have various disadvantages. Automobile manufacturers have sought to obtain a better quality of brake fluid which would also provide a higher factor of safety.
One of the disadvantages of the glycol based polyether brake fluids is the rather limited high temperature stability of such compositions. Thus, it has been found that at some temperatures to which the brake system of an automobile may conceivably be exposed, these brake fluids may degrade or evaporate. It has also been found that at such high temperatures these brake fluids may possibly vaporize, thereby causing spontaneous brake failure. Thus, the brake fluids presently on the market tend to have an undesirable low boiling point.
Another disadvantage of the glycol based polyether brake fluids presently on the market is that they are hygroscopic, that is, such fluids tend to pick up water and moisture from the air quite easily. Although such glycol based polyether brake fluids have the property of being compatible with large amounts of water, nevertheless, due to their hygroscopicity they will over a period of time absorb a large amount of moisture into the system, such that when the compatibility level of the water in the polyether glycol based fluid is exceeded the water will cause undesirable changes in the physical properties of the brake fluid. At low temperatures such large amounts of absorbed water in the polyether glycol based brake fluid will undesirably increase the viscosity of the brake fluid and deleteriously affect the performance of the brakes. At high temperatures the presence of large amounts of water may result in the water being vaporized to create what is known as vapor-lock in the hydraulic lines of the brake system, which also results in improper performance of the brakes.
To overcome these disadvantages of the presently available brake fluids, manufacturers have sought other types of fluids which would have a higher performance factor in automobile brake systems, and which avoid the disadvantages of the glycol based polyether brake fluids mentioned above.
Several silicone fluids have been proposed for use as brake fluids. Silicone fluids have the particular advantage of a very high flash point and do not degrade at high temperatures thus retaining their chemical stability. In addition, silicone fluids also have a high fire point. Even during periods of exceptional stress in the operation of the hydraulic brake system of an automobile the temperature reached in the hydraulic system is considerably below the flash point and fire point of such silicone fluids. Additionally, silicone fluids advantageously exhibit a desirably small viscosity at low temperatures, even at temperatures as low as -40.degree. C. Furthermore, most silicone fluids are not hygroscopic and take up very little water or moisture from the air and are not ordinarily associated with problems of excessive water absorption. However, since water may conceivably enter the system by accident or some other means, it is desirable that a silicone fluid be compatible with a reasonable amount of water. Thus, silicone hydraulic fluids can be modified in order to be compatible with reasonable amounts of water.
In addition, it is desirable to obtain a silicone fluid which has a pourable viscosity at low temperatures and yet has a minimum viscosity high operating temperature.
The necessity for a low viscosity of the brake fluid at low temperatures is so that such a fluid can be used in very cold climates and even in the arctic regions.
In addition, it is desired that the silicone fluid that is to be used as a brake fluid be compatible with the common brake fluids presently on the market, that is, the glycol based polyether fluids. Thus, if by accident some non-silicone brake fluid enters the system or if silicone fluid is added by accident to a hydraulic braking system to replace some glycol based polyether fluid, then it is desirable that the silicone fluid be compatible with the glycol based polyether fluid.
While the above discussion has been directed to the use of a silicone polymer as a brake fluid, it should be mentioned that a silicone fluid having the above-named advantages over glycol based polyether fluids would be a superior hydraulic fluid for use in hydraulic systems. Such a hydraulic system may or may not include a hydraulic reservoir; it would include a mechanical hydraulic activating means which may for instance be a brake pedal to which mechanical pressure is applied; and it would also include a hydraulic activated means which may be the pistons or other types of mechanisms that are activated by the hydraulic pressure in the brake drum shoe or disc brake or other type of hydraulic system assembly. The hydraulic activating means, hydraulic activated means and hydraulic reservoir are all connected by the necessary hydraulic lines. Thus, it is not intended to limit the application of the novel silicone polymer fluid disclosed in this application solely for use in brake hydraulic systems but such a fluid may be used in all types of known hydraulic systems and would have the superior advantages and properties of silicone fluids as well as the specific advantages mentioned above.
Accordingly, it is one object of the present invention to provide a novel silicone polymer fluid which is useful as a hydraulic fluid.
Another object is to provide a silicone hydraulic fluid which is particularly effective for use in automotive braking systems.
Another object is to provide a silicone brake fluid which is primarily a methylsiloxane base fluid exhibiting mono-, di-, and tri-functional polymeric units, which is combined with an alkoxy functional siloxane copolymer.
Another object is to provide a silicone brake fluid which incorporates rubber swell, anti-oxidant, and anti-corrosive additives as well as dyes for color.
Another object is to provide a process for producing the abovedescribed silicone brake fluids.
Another object is to provide a hydraulic system utilizing such silicone brake fluids.
These and other objects will become apparent to one skilled in the art upon consideration of the following detailed specification.